When forming a multilayer interconnection in a semiconductor integrated circuit (LSI), a metal cap film may selectively be formed on a Cu wire to prevent diffusion of copper (Cu) or Cu alloys (hereinafter, referred to together as Cu) used as a wire material into a low-k film in an upper layer and also to improve adhesion properties of the low-k film. Such a metal cap technology is expected to be needed in the future in preparation for higher performance of a multilayer interconnection. A major candidate material of a metal cap film is a CuSiN film, which is a compound film of Cu, silicon (Si) and nitrogen (N) or a CuSix film, which is a silicide film with Cu (see Published Unexamined Japanese Patent Application (JP-A) No. 2006-261440 or JP-A-2007-27769, for example). The CuSiN film and CuSix film are excellent, as described above, in terms of barrier properties against Cu and therefore can achieve the effect of suppressing transport of Cu atoms on the Cu surface. Accordingly, electromigration characteristics can be improved. On the other hand, however, problems related to higher wire resistance arise.